1. Field of the Invention
The present invention relates to the construction of a connecting part, or connector, between the ignition plug and the ignition cable in an internal combustion engine, such as an automobile.
2. Description of Background Information
Depending on the layout of the internal combustion engine, such as an engine in an automobile, there may be times in which a heat generating member, e.g., an exhaust pipe or radiator, is positioned very close to the engine body. In fact, the heat which is generated in that area is often greater than 400.degree. C. In such a cases, it is critical that the structure of the connection between the ignition cable and the ignition plug fixed to the engine body take into account the need to provide adequate countermeasures against such heat.
Accordingly, a conventional construction of the connecting part is shown in FIG. 6 and FIG. 7.
That is to say, the structure of the connecting part is such that a high voltage terminal T of the ignition cable K end is contained in a rubber boot 100. The rubber boot 100 is engaged with an insulator part Pg of an ignition plug P projecting from the engine body E, by which the high voltage terminal T and the end terminal Pt on the upper part of the insulator Pg are held in an electrically connected state. Additionally, the rubber boot 100 is covered with a metal heat shielding member 110, thereby preventing thermal degradation of the rubber boot 100.
Further, since a high voltage may be induced to the heat shielding member 110 by a secondary high voltage which provides the spark to the ignition plug P, the member 110 must be grounded. Therefore, the upper end of an electrically conductive coil spring 112 is engaged at the opening at the bottom end of the heat shielding member 110. The bottom end of the coil spring 112 projects downwardly from the heat shielding member 110, so that at the time of engagement of the rubber boot 100 with the insulator Pg, the coil spring 112 is brought into contact with the outer peripheral metal part 114 of the ignition plug P to provide the necessary ground.
However, according to the conventional construction of the connecting part as described above, in engaging the rubber boot 100 with the insulator Pg, the coil spring 112 interferes with the insulator Pg of the ignition plug P. Accordingly, the assembly process is inhibited, and due to the insufficient engagement between the rubber boot 100 and the insulator Pg, electrical connection between the high voltage terminal T and the end terminal Pt becomes imperfect, thus giving rise to a risk of inducing accidental firing of the ignition plug or stoppage of the engine.
Also, because of the configuration of the outside of the rubber boot 100 to be covered by the heat shielding member 110, the construction of the connecting part must be greater in size. This leads to aggravation of assembly work in a narrow space surrounded by exhaust pipes and the like, and to an imperfect electrical connection between the high voltage terminal T and the end terminal Pt caused by incomplete engagement between the rubber boot 100 and the insulator Pg, which may result in accidental firing of the ignition plug or stoppage of the engine.
Furthermore, according to the construction of the connecting part as above, by pressing downwardly on the upper end of the rubber boot 100, the rubber boot 100 is to be engaged with the insulator part Pg. However, since the rubber boot per se has low rigidity, and since it is surrounded by a metal heat shielding member 110, no moderate feel is provided at the time of the engagement. Therefore, assembly is apt to be terminated prior to complete engagement between the rubber boot 100 and the insulator part Pg. Thus, the resulting incomplete electrical connection between the high voltage terminal T and the end terminal Pt gives rise to a risk that the engine will be accidentally fired or stopped.
Accordingly, the present invention has been made to resolve the problems described above, and its object is to provide a construction of the connecting part between the ignition plug and the ignition cable so that it is possible to provide a more secure connection between the connection terminal on the ignition cable side.